In forming photoreceptor belts lamination may be employed by applying alternate layers of thermoplastic sheets and reinforcing fabrics. Another method of forming said belts is by molding which unfortunately often results in flashing that requires removal to achieve a smooth outer surface.
In employing the coating technique the belt is mounted on a mandrel and coated with a single or multiple layer polymeric or non-polymeric having a solvent base to provide a seamless belt. During the coating process the belt and the mandrel are subjected to several heating and cooling steps.
More recently these belts have been formed by applying uniform fluid coating of polymeric film on a cylindrical mandrel, solidifying the fluid coating to form a uniform solid coating and separating the uniform solid coating from the mandrel. During the forming step, both the mandrel and the belt are subjected to a heating step that results in expansion of the coating and the mandrel.
Where the coating step involves solvent soluble polymers, solvent evaporation from the coated solution can cause significant cooling of the belt substrate. After each coating process the mandrel and belt are cycled through a heated oven to remove residual solvents. This cooling and heating effect can have adverse effects on the belt formed because the seamless belt and the mandrel have different thermal characteristics. The problem is that the mandrel made of solid metal, solid plastics or flexible metal, has thermal characteristics that do not match those of the belt. As a result, the uniform contact between the belt and the mandrel is not always maintained. Consequently, the desired structural uniformity is also deficient.
The film forming polymer material is deposited in fluid form, preferably by spraying on the mandrel. The coating is then heated to drive off residual solvent. The effect when using a metal mandrel causes the belt with its coating to expand more than the mandrel. Upon cooling the belt with coating will contract at a rate greater than that of the metal mandrel. Because of the differences in expansion and contraction, contact between the belt and the mandrel is not necessarily maintained in a consistent manner.
If the belt substrate is not held in a relatively constant disposition relative to the mandrel, the deposition may be distorted. Similarly, where thermal characteristics are uneven, uniformity may be lost in coating. In both instances the belt ultimately formed may have inconsistent electrical characteristics, adversely affecting the copier performance. These problems can occur regardless of the deposition technique used.